The purpose of this study was to show the viability of a 0.70 m3 three phase aerobic fluidized bed bioreactor for the denitrification of wastewater by anammox bacteria. The reactor was monitored for 343 days, operating in a batch mode for 50 days, with a continuous flow of wastewater being fed for the remaining 293 days. It was determined that anammox contributed up to 5.5±0.5% of the ammonia removal during the batch mode of operation, and up to 14.2±3.7% of the ammonia removal during the continuous mode of operation. The highest ammonia and total nitrogen removals of 90.9±1.6% and 20.8±4.1% were measured under high recycle rates. Up to 63.1±5.2% and 19.2±7.5% ammonia and total nitrogen removal was observed after a single pass through the reactor. At low COD concentrations and anoxic conditions, ammonia and nitrite were removed simultaneously. Under the evaluated conditions, the reactor was determined to contain anammox bacteria.